Biologists Look At Enzymes

In a practical experiment, A Level Biology students have been investigating the effect of temperature on the activity of lipase. For this, they tested skimmed and full-fat milk by adding phenolphthalein to their samples, which immediately turned them pink.

The girls recorded the time it took for the reagent and pH indicator to turn the liquid colourless as the pH dropped. The quicker the reaction, the more rapidly the enzyme was working to break down the fat in the milk into fatty acids.

Did the amount of fat in the milk make any difference to the speed of the colour change? Also, did variable temperatures affect the results?